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From: roy@phri.UUCP (Roy Smith)
Newsgroups: net.unix-wizards
Subject: Just how reliable is NFS?
Message-ID: <2428@phri.UUCP>
Date: Mon, 8-Sep-86 10:51:41 EDT
Article-I.D.: phri.2428
Posted: Mon Sep  8 10:51:41 1986
Date-Received: Tue, 9-Sep-86 05:44:57 EDT
References: <6@cvbnet.uucp> <335@mc0.UUCP>
Reply-To: roy@phri.UUCP (Roy Smith)
Organization: Public Health Research Inst. (NY, NY)
Lines: 26
Keywords: UDP, NFS, checksums
Original-Subject: Re: simultaneous file transfer on ethernet (SUN's)


In article <6@cvbnet.uucp> acrotty@cvbnet.uucp (Art Crotty) asked about
broadcasting a file to all the nodes on an ethernet.

In article <335@mc0.UUCP> garyf@mc0.UUCP (Gary Friedman) explained that
TCP/IP guarantees safe delivery for point-to-point links and that UDP
allows for broadcasting, but at the price of reduced reliability.  Gary
then suggests that Art probably wants to use NFS, since it's designed to
allow efficient sharing of a file by many hosts.

	Clearly, UDP is not suitable for times when you really care if the
data gets delivered or not (rwho uses UDP, doesn't it?).  As I understand
it, NFS uses UDP as the underlying transport protocol but to improve
performance, Sun has turned off checksumming in NSF/UDP packets.
Presumably NFS does its own error checking at a higher level, so they can
get away with ignoring checksums at the lower levels.

	Has anybody done any studies to determine if this causes any
problems?  I've heard random comments by people on the net that they don't
like what Sun did, but has anybody taken a serious look at the situation
and found cases where corrupted UDP packets have caused user-visible NFS
errors?  On the other hand, has anybody made any measurements to see just
how much NFS would be slowed down if UDP checksumming were turned back on?
-- 
Roy Smith, {allegra,philabs}!phri!roy
System Administrator, Public Health Research Institute
455 First Avenue, New York, NY 10016